1. Technical Field
This application relates to intervertebral distracting instruments, intervertebral disc implants, and a method for inserting intervertebral disc implants between affected vertebrae to achieve spinal fusion.
2. Background of Related Art
The human spine is composed of thirty-three vertebrae at birth and twenty-four as a mature adult. Between each pair of vertebrae is an intervertebral disc, which maintains the space between adjacent vertebrae and acts as a cushion under compressive, bending, and rotational loads and motions. A healthy intervertebral disc has a great deal of water in the nucleus pulposus, which is the center portion of the disc. The water content gives the nucleus a spongy quality and allows it to absorb spinal stress. Excessive pressure or injuries to the nucleus can cause injury to the annulus, which is the outer ring that holds the disc together. Generally, the annulus is the first portion of the disc that experiences injury. These injuries are typically in the form of small tears. These tears heal by scar tissue. The scar tissue is not as strong as normal annulus tissue. Over time, as more scar tissue forms, the annulus becomes weaker. Eventually this can lead to damage of the nucleus pulposus. The nucleus begins to lose its water content due to the damage, i.e., it begins to dry up. Because of water loss, discs lose some of their ability to act as a cushion. This can lead to even more stress on the annulus and still more tears as the cycle repeats. As the nucleus loses its water content it collapses, allowing the vertebrae above and below the disc space to move closer to one another. This results in a narrowing of the disc space between the two vertebrae. As this shift occurs, the facet joints located at the back of the spine are forced to shift. This shift changes the way the facet joints work together, and thus, can cause problems in the facet joints as well.
When a disc or vertebra is damaged due to disease or injury, standard practice is to remove all or part of the intervertebral disc, insert a natural or artificial disc spacer, and construct an artificial structure to hold the affected vertebrae in place to achieve a spinal fusion. The procedure may be accomplished using various approaches such as anteriorly, posteriorly and transforaminally. Depending on which approach is used, a specific geometry spacer device is selected.
Anteriorly approached procedures are preferred when one of the clinician's goals is to use a spacer device that most closely matches the footprint of the vertebral body. This maximum sized footprint also allows for the introduction of a significant amount of bone graft. It may also promote a better bone fusion. The preferred instrument to introduce an anterior spacer device is a “sled” style instrument. The sled provides the necessary vertebral body distraction and a path for introducing the device. Unfortunately, the sleds currently available are very bulky, complicated to use, and obstruct the clinician's working view.
For the above stated reasons, a need exists for a system that includes an instrument for distracting the vertebral bodies in such a way that does not obstruct the surgeon's view and still allows additional disc space work to be performed. The system must also provide a pathway for introducing the device into the intervertebral disc's space.